Thixotropic polymerizable composites that are light curable and that contain polymerizable organic monomeric materials combined with inorganic fillers are commonly used as materials in restorative and prosthetic dental procedures. These dental materials are generally blends of polymerizable organic monomeric materials, inorganic fillers (the inorganic fillers providing structural reinforcement for the composite), and a photoinitiating system that includes a photoinitiator and photoreducers such as tertiary amines. More specifically, these dental compositions typically include a mixture of acrylate-based polymerizable monomeric materials such as methyl methacrylate, particulate fillers such as hydroxyapatite, camphorquinone as a photoinitiator, and tertiary amines as polymerization cofactors. These mixtures are non-aqueous and have like a paste-like consistency until they are hardened by polymerization.
In performing these dental procedures, these polymerizable composites are typically applied to a target area in the oral cavity, where the polymerizable composites is needed, and then shaped or combined with a dental prosthetic that is to be bonded to a dental target. When the procedure advances to a point where the polymerizable composite can be cured, a light source is introduced and the polymerizable composite is irradiated to activate the camphorquinone photoinitiator, which absorbs light and is promoted to an excited state. The activated photoinitiators can interact with photoreducers to initiate free radical addition polymerization of the monomeric materials in the dental composites, thereby promoting the hardening of the composite. The mixture typically hardens relatively rapidly, in about 20-60 seconds.
Because of the widespread use of visible light activated photoinitiators such as camphorquinone in polymerizable dental composites, lamps specifically useful for promoting the activation of this molecule for hardening the mixtures are commonly found in places where dental procedures are carried out. Since camphorquinone optimally absorbs, and is activated by light in range of about 440 nm to 500 nm (with a maximum absorbance of about 470 nm), lamps or other light sources having this emission spectrum are preferably used. Although argon-ion lasers can be used to activate photoinitiators such as camphorquinone, plasma arc, conventional halogen lamps, fast halogen lamps, and more commonly LED (light emitting diode) sources are used as activating light sources. LED sources can emit radiation over a narrow spectrum coincident with the maximum absorbance of camphorquinone, and generally do not produce excessive heat. It is noted that the photoinitiation mechanism that is provided by a camphorquinone/LED system is relatively weak as compared to photoinitiation systems that use short wavelength UV (e.g., UVA) activated photoinitiators in conjunction with high intensity low-UV emitting light sources, such as metal halide bulbs.
The polymerization of materials in dental composites is generally improved by the physical properties of a thixotropic composition, and the presence of ancillary agents, such as photoreducers or accelerants. Given this, polymerizable compositions that are non-thixotropic (for example, aqueous compositions) are not commonly used for dental procedures.
While the physical properties of thixotropic compositions are particularly amenable to dental procedures, the chemical characteristics of these compositions may be less than desirable. Some small molecular weight compounds present in dental compositions, such as monomeric materials and ancillary reagents, may present toxicity concerns. If not completely consumed in the polymerization reaction, these monomeric materials may leach out of the composite. Furthermore, the solvent systems used in thixotropic compositions, especially those having an organic component, may be less than ideal for oral use.
While thixotropic compositions are commonly used for restorative and prosthetic dental procedures, these compositions are generally not used for the treatment of degeneration of hard tissue such as bone, or softer tissue such as cartilage. Such degenerative conditions are often seen in periodontitis, which is a chronic infective disease of the gums caused by bacteria present in dental plaque. This condition induces the breakdown of the tooth supporting apparatus until teeth are lost. Surgery may be indicated to arrest disease progression and regenerate lost tissues. Several surgical techniques have been developed to regenerate periodontal tissues including guided tissue regeneration (GTR), bone grafting (BG) and the use of enamel matrix derivative (EMD).
The present invention relates to novel polymerizable systems and methods that can be used to address challenges associated with tissue regeneration. While the inventive compositions and methods described herein are particularly useful for dental purposes, they can also be used to treat other medical conditions.